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THINKING CRITICALLY Are Personality Traits Inherited

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THINKING CRITICALLY Are Personality Traits Inherited
430
FIGURE
Chapter 11 Personality
11.3
Eysenck’s Personality Dimensions
Emotional
According to Eysenck, varying
degrees of emotionalityby
stability and introversionextraversion combine to produce
predictable trait patterns. Which section of
the figure do you think best describes your
personality traits? How about those of a
friend or a relative? Did you find it any
easier to place other people’s personalities in a particular section than it was to
place your own personality? If so, why do
you think that might be?
Moody
Anxious
Rigid
Sober
Pessimistic
Reserved
Unsociable
Quiet
doing
2
learn
Touchy
Restless
Aggressive
Excitable
Changeable
Impulsive
Optimistic
Active
Introverted
Extraverted
Sociable
Outgoing
Talkative
Responsive
Easygoing
Lively
Carefree
Leadership
Passive
Careful
Thoughtful
Peaceful
Controlled
Reliable
Even-tempered
Calm
Stable
Source: Eysenck & Rachman (1965).
stem from two related systems in the brain. These are called the behavioral approach
system and the behavioral inhibition system (Pickering & Gray, 1999). The behavioral
approach system, or BAS, is made up of brain regions that affect people’s sensitivity to
rewards and their motivation to seek these rewards. The BAS has been called a “go”
system because it is responsible for how impulsive or uninhibited a person is. The
behavioral inhibition system, or BIS, includes brain areas that affect sensitivity to possible punishment and the motivation to avoid being punished. The BIS is a “stop” system that is responsible for how fearful or inhibited a person is. Gray says that people
with an active behavioral approach system tend to experience positive emotions; people with an active behavioral inhibition system are more likely to experience negative
ones (Larsen & Buss, 2005). Gray’s theory is now more widely accepted than Eysenck’s
theory—primarily because it is supported by what neuroscientists have learned about
brain structures and neurotransmitters and how they operate (Avila, 2001; Franken,
Muris, & Georgieva, 2006; Larsen & Buss, 2005; Wacker, Chavanon, & Stemmler, 2006).
G
T H I N K I N G C R I T I C A L LY
ray’s approach-inhibition theory is
one of several biologically oriented
Are Personality Traits
explanations of the origins of personality traits (e.g., Zuckerman, 2004). A related
Inherited?
approach involves exploring the role of genetics in these traits. For example, consider a pair
of identical twins who had been separated at five weeks of age and did not meet again
for thirty-nine years. Both men drove Chevrolets, chain-smoked the same brand of cigarettes, had divorced a woman named Linda, were remarried to a woman named Betty,
had sons named James Allan, had dogs named Toy, enjoyed similar hobbies, and had
served as sheriff ’s deputies (Tellegen et al., 1988).
431
The Trait Approach
■ What am I being asked to believe or accept?
Cases like this have helped focus the attention of behavioral geneticists on the possibility that some core aspects of personality might be partly, or even largely, inherited
(Bouchard, 2004; Ebstein, 2006; Johnson et al., 2004; Krueger, Markon, & Bouchard,
2003; Noblett & Coccaro, 2005).
■ Is there evidence available to support the claim?
FAMILY RESEMBLANCE Do children
inherit personality traits in the same direct way as they inherit facial features,
coloration, and other physical characteristics? Research in behavioral genetics suggests that personality is the joint product
of genetically influenced behavioral tendencies and the environmental conditions
each child encounters.
Some of the evidence for this assertion comes from the many familiar cases in which
children seem to “have” their parents’ or grandparents’ bad temper, generosity, or shyness. More systematic studies have also found moderate but significant correlations
between children’s personality test scores and those of their parents and siblings (Davis,
Luce, & Kraus, 1994; Loehlin, 1992).
Even stronger evidence comes from studies conducted around the world that compared identical twins raised together, identical twins raised apart, nonidentical twins
raised together, and nonidentical twins raised apart (Grigorenko, 2002). Whether they are
raised apart or together, identical twins (who have exactly the same genes) tend to be
more alike in personality than nonidentical twins (whose genes are no more similar than
those of other siblings). This research also shows that identical twins are more alike than
nonidentical twins in general temperament, such as how active, sociable, anxious, and
emotional they are (Pickering & Gray, 1999; Borkenau et al., 2002; Wolf et al., 2004). On
the basis of such twin studies, behavioral geneticists have concluded that at least 30 percent, and perhaps as much as 60 percent, of the differences among people in terms of
personality traits is due to genetic factors (Caspi, Roberts, & Shiner, 2005).
■ Can that evidence be interpreted another way?
Family resemblances in personality could reflect inheritance or social influence. So an
obvious alternative interpretation of this evidence might be that family similarities
come not from common genes but from a common environment. Children learn many
rules, skills, and behaviors by watching parents, siblings, and others; perhaps they learn
their personalities as well (Funder, 2004). And the fact that nontwin siblings are less
alike than twins may well result from what is called nonshared environments (Plomin,
2004). Nonshared factors include, for example, a child’s place in the family birth order,
differences in the way parents treat each of their children, and accidents, illnesses, or
events that alter a particular child’s life or health (Paulhus, Trapnell, & Chen, 1999).
Nontwins are more likely than twins, especially identical twins, to be affected by these
nonshared environmental factors.
■ What evidence would help to evaluate the alternatives?
One way to evaluate the idea that personality is inherited would be to locate genes that
are associated with certain personality characteristics (Ebstein, 2006). Genetic differences have already been tentatively associated with certain behavior disorders, but most
behavioral genetics researchers doubt that there are direct links between particular
genes and particular personality traits (Caspi et al., 2005; Reif & Lesch, 2003).
Another way evaluate the role of genes in personality is to study people in infancy,
before the environment has had a chance to exert its influence. If the environment were
entirely responsible for personality, newborns should be essentially alike. However, as
discussed in the chapter on human development, infants show immediate differences
in activity level, sensitivity to the environment, the tendency to cry, and interest in new
stimuli (Rothbart & Derryberry, 2002). These differences in temperament suggest biological, and perhaps genetic, influences.
To evaluate the relative contributions of nature and nurture beyond infancy, psychologists have examined the personality characteristics of adopted children. If adopted
children are more like their biological than their adoptive parents, this suggests the
influence of heredity in personality. If they are more like their adoptive families, a
strong role for environmental factors in personality is suggested. In actuality, adopted
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